1. Field of the Invention
This invention relates generally to vehicle-mounted drilling rigs for wells and the like, and more particularly to the derrick or mast for a relatively light-weight, truck-mounted rig.
2. Description of the Prior Art
Truck-mounted drilling rigs are well known and widely used They range in size and capacity from a relatively small and light-weight, truck-mounted unit as shown in U.S. Pat. No. 2,410,959 to a relatively large and heavy unit mounted on a track-laying vehicle as shown in U.S. Pat. No. 3,867,989. In many cases, the drilling rig includes a multi-section derrick similar in appearance to that shown in U.S. Pat. No. 3,867,989, which is an assembly of several lengths of structure which are normally transported on the truck in a horizontal attitude, but then assembled end to-end at the drilling site and raised to a vertical attitude for the drilling operation. These derricks include winches, cables and sheaves to raise and lower the drilling bit and attached string of pipe, and to force the drill into the ground, using the weight of the derrick and the rear end of the transporting truck to apply the downward load onto the drill bit. These structures are rather complicated, heavy, have many working components exposed to the environment, have a generally cluttered appearance and are expensive. It is therefore a general object of the present invention to provide a well drilling rig overcoming some of these disadvantages of the prior art.